This invention relates to zinc plating baths, and particularly to acid or alkaline zinc plating baths for plating bright and level zinc deposits on substrates. More particularly, the plating baths of the invention contain a polymeric nitrogen-containing compound prepared by reacting a poly(alkyleneimine) with a cyclic carbonate consisting of carbon, hydrogen and oxygen atoms.
The invention also relates to a method of electrodepositing bright zinc coatings on a substrate.
Considerable attention has been directed to the development of zinc electroplating baths which will produce bright and level zinc deposits of improved quality. Research has been devoted primarily to improving the overall brightness, the range of allowable current densities, and the ductility of the zinc deposit. The electroplating baths which have been developed are either acid zinc solutions or alkaline zinc solutions. Many of the alkaline zinc plating baths which have been suggested and used in the past contain cyanide. Because of the enactment and enforcement of various environmental protection laws, especially those designed to improve water quality, pressure on the industry has resulted in a reduction in the use of alkaline cyanide-containing plating baths.
Typically, acid zinc plating baths have been based on a suitable inorganic zinc salt such as zinc sulfate, zinc chloride, zinc fluoborate, zinc acetate, zinc sulfamate or zinc pyrophosphate. The bath usually includes a buffer such as the corresponding ammonium salt and other additives to promote an improved ductility, brightness, throwing power and covering power. Surface active agents may be included to improve the crystal structure, reduce pitting and increase the solubility of the other additives.